(1) Field of the Invention
The invention concerns an electrical battery that is in particular intended for electrical or hybrid motor vehicle traction, that is to say comprising an electric motor driving the driven wheels combined with a thermal engine driving these wheels or possibly other driven wheels.
(2) Prior Art
In particular, the invention applies to a high degree of hybridisation of thermal vehicles which may go as far as complete electrification of the traction chain. In this case, the batteries do not then merely serve to assist the vehicles in the acceleration phases but also to provide movement of the vehicle autonomously over greater or lesser distances.
To guarantee the levels of power and energy required for the applications in question, it is necessary to create batteries comprising a plurality of electrical energy generating elements.
However, when these elements are charged and discharged, the result is a production of heat which, when it is not controlled, may have the effect of reducing the service life of the elements, or even giving rise, under extreme conditions, to risks of thermal runaway for certain chemical components of elements, leading to deterioration of the battery.
Thus, in order to optimize the performance and service life of the batteries, thermal conditioning systems for the elements are integrated in the batteries. In particular, the thermal conditioning systems may comprise a circulation path for a thermal conditioning liquid, said path being formed essentially around the generating elements.
In addition, in the automobile application envisaged, the efficacy of the systems must be high since the thermal dissipation peaks depend on the current densities and their variations, which may reach very high values, in particular during phases of high acceleration, regenerative breaking, rapid discharges of the battery or motorway functioning in electrical mode.
The generating elements conventionally comprise at least one electrochemical cell, for example of the lithium-ion or lithium-polymer type, which is formed by a stack of electroactive layers acting successively as cathodes and anodes, said layers being put in contact by means of an electrolyte.
These electrochemical cells are generally packaged in rigid, hermetically sealed containers in order to protect them from external attacks. In particular, these containers may be manufactured from deep-drawn metal sheets in order to form cups which, after the introduction of a winding of stacked layers, can be closed by welding of a cover.
This type of packaging has certain drawbacks, including high manufacturing costs as well as the need to electrically insulate at least one of the electrodes of the metal cup and to add discharge valves for releasing the pressure in the event of overcharging or overheating of an element.
To resolve these drawbacks, it has been proposed to form a generating element by packaging a flat stack of electroactive layers in a sealed flexible envelope. In addition, this type of generating element typically has a prismatic geometry that increases the exchange surfaces with the thermal conditioning liquid.
However, with such an envelope, the mechanical strength of the elements is significantly weakened, which runs counter to the current constraints in the automotive industry, in particular relating to crashes.
In addition, the stack is then liable to deform, in particular with movements of the layers with respect to one another. In particular, such a deformation may be caused by the change in the volume of the active materials serving as anodes or cathodes according to its lithium-ion insertion rate.
The result of these movements is variations in the contact resistances between said layers, said variations producing additional heating that may lead to premature aging, a limitation to the energy available and risks of triggering of thermal runaway.